Details of a Researcher - Ishigure, Takaaki

Papers - Ishigure, Takaaki

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Analysis of interchannel crosstalk in multimode parallel optical waveguides using the beam propagation method

Takuya Kudo and Takaaki Ishigure

Optics Express 22 ( 8 ) 9675 - 9686 2014.04

Research paper (scientific journal), Joint Work, Accepted

We theoretically analyze the origin of inter-channel crosstalk in
densely aligned multimode parallel optical waveguides for on-board
interconnects using the Beam Propagation Method. In this paper, we
demonstrate that the inter-channel crosstalk due to mode coupling is very
low in graded-index (GI) circular-core waveguides because the propagation
constants of the propagating modes are discrete. Additionally, it is also
found that the waveguides with GI-type circular cores is sensitive to the
optical confinement in the cladding: low-power cladding modes largely
decrease the mode conversion.

Accurate interchannel pitch control in graded-index circular-core polymer parallel optical waveguide using the Mosquito method

Ryota Kinoshita, Daisuke Suganuma, and Takaaki Ishigure

Optics Express 22 ( 7 ) 8426 - 8437 2014.04

Research paper (scientific journal), Joint Work, Accepted

We successfully fabricate polymer optical waveguides with graded-index (GI) circular cores whose diameter and interchannel pitch are accurately controlled using the Mosquito method: GI-core waveguides with 250-, 125- and 62.5-μm pitches are successfully obtained. The Mosquito method utilizing a microdispenser is a very simple technique for fabricating GI-circular-core polymer optical waveguides. The accurately controlled pitch is confirmed by a high connectivity with a commercially available multimode fiber (MMF) ribbon with a 125-μm pitch. Furthermore, by inserting the waveguide between two 12-channel MMF ribbons, we experimentally demonstrate 11.3 Gbps × 12 Ch. parallel signal transmission through a GI-core waveguide with a 125-μm pitch for the first time to the best of our knowledge.

Polymer Optical Waveguides With GI and W-Shaped Cores for High-Bandwidth-Density On-Board Interconnects

Ryota Kinosita, Kimio Moriya, Koji Choki, and Takaaki Ishigure

Journal of Lightwave Technology (IEEE/OSA) 31 ( 24 ) 4004-4015 2013.12

Research paper (scientific journal), Joint Work

We fabricate polynorbornene-based graded-index
(GI) core polymer optical waveguides using the photoaddressing method, and demonstrate that the GI-core polymer waveguides are capable of realizing high-bandwidth-density on-board optical interconnects. Because of the tight optical confinement effect of the parabolic refractive index profile, the fabricated GI-core polymer waveguides exhibit superior optical properties compared to stepindex (SI) core polymer waveguides: low propagation loss, low connection loss with GI multimode fiber (MMF) with wide misalignment tolerance, and low interchannel crosstalk even under a small pitch size are experimentally confirmed. Furthermore, interchannel crosstalk due to multicore operation is experimentally evaluated, and a method to estimate the interchannel crosstalk in multimode polymer parallel optical waveguides under multicore
operation is proposed for the first time, to the best of our knowledge. The photoaddressing method capable of fabricating even low-loss GI-core polymer waveguide circuits will pave the way for realizing low-cost and high-bandwidth-density optical printed circuit boards.

Photonic bandgap Bragg fiber sensors for bending/displacement detection

Hang Qu, Tiberius Brastaviceanu, Francois Bergeron, Jonathan Olesik, Ivan Pavlov, Takaaki Ishigure, and Maksim Skorobogatiy

Applied Optics (OSA) 52 ( 25 ) 6344-6349 2013.09

Research paper (scientific journal), Joint Work, Accepted

We demonstrate an amplitude-based bending/displacement sensor that uses a plastic photonic bandgap
Bragg fiber with one end coated with a silver layer. The reflection intensity of the Bragg fiber is
characterized in response to different displacements (or bending curvatures). We note that the Bragg
reflector of the fiber acts as an efficient mode stripper for the wavelengths near the edge of the fiber
bandgap, which makes the sensor extremely sensitive to bending or displacements at these wavelengths.
Besides, by comparison of the Bragg fiber sensor to a sensor based on a standard multimode fiber
with similar outer diameter and length, we find that the Bragg fiber sensor is more sensitive to bending
due to the presence of a mode stripper in the form of a multilayer reflector. Experimental results show
that the minimum detection limit of the Bragg fiber sensor can be as small as 3 μm for displacement
sensing.

Analysis of Connection Loss for a GI Waveguide Based Optical Link Using the Finite Difference Beam Propagation Method

HSU HSIANG-HAN, ISHIGURE TAKAAKI, NAKAGAWA SHIGERU

Journal of Lightwave Technology (IEEE/OSA) 31 ( 12 ) 2036-2042 2013.06

Research paper (scientific journal), Joint Work, Accepted

The connection loss which occurs when light transfers
from one medium to another attracts additional attention in highspeed and low-power optical links. In this paper, we not only experimentally apply graded index polymer optical waveguide (GIPOW) in the optical link, but also theoretically address some key parameters which largely influence on the connection loss. The experimental setup of this optical link is composed of a VCSEL module, a GI polymer optical waveguide for the transmitter side(WGTx), a GI multimode fiber (GI-MMF), a GI polymer optical waveguide for the receiver side (WGRx), and a detector. We assume that WGTx is launched by a single mode fiber and then measure the connection losses at the interface between any two components. The results show the connection loss between the GI-MMF and the WGRx is approximately 0.4 dB higher than that of the WGTxto theGI-MMF. For the theoreticalmodeling, we start from the fundamental scalar wave equation, and apply the finite difference beam propagation method (FD-BPM) to simulate the behavior of light inside the waveguide. Furthermore, Fresnel reflection between two media and the scattering effect within polymer optical waveguides are also taken into account. The simulated results show a similar trend to the measured values. Finally, we conclude that the scattering effect could be one of the key issues of GI-POW for maintaining low connection losses with other waveguides
and fibers.

Fabrication of a Graded-Index Circular-Core Polymer Parallel Optical Waveguide Using a Microdispenser for a High-Density Optical Printed Circuit Board

SOMA KAZUTOMO 　ISHIGURE TAKAAKI

IEEE Selected Topics in Quantum Electronics (IEEE) 19 ( 2 ) 3600310 2013.04

Research paper (scientific journal), Joint Work, Accepted

A simple fabrication method for multimode polymer optical waveguides with graded-index (GI) circular cores is introduced for use in optical printed circuit boards (O-PCBs). The new method, named “Mosquito method,” utilizes a microdispenser to dispense a viscous monomer directly onto the substrates. By optimizing the dispensing conditions, 12-channel parallel waveguides with circular GI-cores (core diameter of 40 μm) are successfully fabricated using the Mosquito method. The advantages of GI-core waveguides for O-PCB applications are discussed by comparing the optical characteristics of the fabricated waveguides with those of conventional step-index (SI) square-core polymer waveguides, and even with those of silica-based GI multimode fibers (MMFs), as an ideal case. To the best of our knowledge, this is the first comparison of SI- and GI-core multimode polymer waveguides that are composed of the same polymer materials and that have similar core and pitch sizes. We experimentally demonstrate that the GI circular-core polymer waveguides fabricated by the Mosquito method have sufficiently low propagation loss (0.033 dB/cm at 850 nm), low connection loss with GI-MMFs, and low interchannel crosstalk. We observe approximately −50 dB of interchannel crosstalk in the 250-μm pitch GI-core waveguide fabricated, which is almost 10 dB lower than in the SI counterpart. Furthermore, sufficiently low crosstalk is maintained in a half-pitch GI-core waveguide fabricated by the Mosquito method.

Carbon nanotube/polymer composite coated tapered fiber for four wave mixing based wavelength conversion

Bo Xu, Mika Omura, Masato Takiguchi, Amos Martinez, Takaaki Ishigure, Shinji Yamashita, and Takahiro Kuga

Optics Express (OSA) 21 ( 3 ) 3651-3657 2013.02

Research paper (scientific journal), Joint Work, Accepted

Brillouin Gain Spectrum Characteriza-tion in Perfluorinated Graded-Index Polymer Optical Fiber with 62.5-μm Core Diameter

MIZUNO YOSUKE, ISHIGURE TAKAAKI，NAKAMURA KENTARO

IEEE Photon. Technol. Lett., (IEEE) 23 ( 24 ) 1863-1865 2011.11

Research paper (scientific journal), Joint Work, Accepted

We characterize the Brillouin gain spectra (BGS) in perfluorinated graded-index polymer optical fibers (PFGI-POFs) with 62.5-μm core diameter. First, we show that the Stokes power is extremely high compared to that of a standard PFGI-POF with 120-μm core, and discuss the Brillouin threshold power. Then, we demonstrate that the PFGI-POF length has little influence on the BGS when the length is longer than 50 m. We also predict that, at 1.55-μm wavelength, it is difficult to reduce the Brillouin threshold power of PFGI-POFs below that of long silica single-mode fibers even if their core diameter is sufficiently reduced to satisfy the single-mode condition. Finally, we confirm the Brillouin linewidth narrowing effect.

Fabrication and inter-channel crosstalk analysis of polymer optical waveguides with W-shaped index profile for high-density optical interconnections

HSU HSIANG-HAN, HIROBE YUSUKE, ISHIGURE TAKAAKI

Optics Express (Optical Society (OSA)) 19 ( 15 ) 14018-14030 2011.07

Research paper (scientific journal), Joint Work, Accepted

For applications in high-density and high-speed optical interconnections, we propose to utilize polymer parallel optical waveguides (PPOWs) with so-called W-shaped refractive index profile in the core area. A W-shaped index profile is composed of a parabolic index distribution surrounded by a narrow index valley, followed by a cladding with a uniform refractive index. We expect that W-shaped index profiles contribute to decreasing the inter-channel crosstalk due to mode conversion in the waveguides. In this paper, we investigate how much the index difference of the index valley improves the crosstalk value. First, we fabricate polymer waveguides with various index profiles by changing the composition of the copolymer for cladding. We show the results that a 1-m long W-shaped profile PPOW has not only low propagation loss (0.027 dB/cm), but an inter-channel crosstalk (~-40 dB) lower than those of graded index (GI) core PPOW we previously fabricated. Next, we theoretically analyze the propagation loss and inter-channel crosstalk in polymer waveguides with different index profiles by means of a ray tracing model in which the light scattering effect is included. The calculation results indicate that the index valley surrounding each core works properly for preventing the power coupling from the cladding modes to the propagation modes, and consequently, very low inter-channel crosstalk is realized with W-shaped index profiles.

Observation of stimulated Brillouin scattering in polymer optical fiber with pump-probe technique

MIZUNO YOSUKE，KISHI MASATO， HOTATE KAZUO,　ISHIGURE TAKAAKI NAKAMURA KENTARO

Optics Letters (Optical Society （OSA)) 36 ( 12 ) 2378-2380 2011.06

Research paper (scientific journal), Joint Work

Stimulated Brillouin scattering (SBS) in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm
core diameter was experimentally observed for the first time, to the best of our knowledge, at 1:55 μm wavelength
with the pump–probe technique. Compared to spontaneous Brillouin scattering previously reported, the Brillouin
gain spectrum (BGS) was detected with an extremely high signal-to-noise ratio, even with a short POF (1m) and
scrambled polarization state. We also investigated the BGS dependences on probe power and temperature, which
indicate that SBS in a POF measured with this technique can be utilized to develop high-accuracy temperature
sensing systems.

GI-core polymer parallel optical waveguide with high-loss, carbon-black-doped cladding for extra low inter-channel crosstalk

UNO HISASHI　/ISHIGURE TAKAAKI

Optics Express (Optical Society (OSA)) 19 ( 11 ) 10931-10939 2011.05

Research paper (scientific journal), Joint Work, Accepted

Graded-index (GI) polymer parallel optical waveguides with high-absorption, carbon-black-doped cladding are fabricated using the preform method in order to reduce the inter-channel crosstalk. The waveguides exhibit a lower inter-channel crosstalk (<-69.3dB) than optically-transparent-clad waveguides (~-33.7 dB) and maintain low propagation loss (0.029dB/cm). We characterize the waveguides with different concentration of carbon black in order to confirm the required concentration (required absorption loss) for keeping the inter-channel crosstalk low enough. In addition, carbon-black-doped waveguides are fabricated directly on a substrate by means of a soft-lithography method. Crosstalk is sufficiently decreased despite the high scattering loss of the core material, while insertion loss is not increased. Furthermore, we fabricate a waveguide with a high-scattering-loss cladding to confirm the origin of low crosstalk in carbon-black-doped waveguides. We confirm that high scattering loss of cladding is not necessarily as effective for crosstalk reduction as high absorption loss of cladding.

Polymer optical waveguide with multiple graded-index cores for on-board interconnects fabricated using soft-lithography

ISHIGURE TAKAAKI　/　NITTA YOSUKE

Optics Express (Optical Society (OSA)) 18 ( 13 ) 14191-14201 2010.06

Research paper (scientific journal), Joint Work

We successfully fabricate a polymer optical waveguide with
multiple graded-index (GI) cores directly on a substrate utilizing the softlithography method. A UV-curable polymer (TPIR-202) supplied from Tokyo Ohka Kogyo Co., Ltd. is used, and the GI cores are formed during the curing process of the core region, which is similar to the preform process we previously reported. We experimentally confirm that near
parabolic refractive index profiles are formed in the parallel cores (more than 50 channels) with 40 μm x 40 μm size at 250-μm pitch. Although the loss is still as high as 0.1 ~0.3 dB/cm at 850 nm, which is mainly due to scattering loss inherent to the polymer matrix, the scattering loss attributed to the waveguide’s structural irregularity could be sufficiently reduced by a graded refractive index profile. For comparison, we fabricate step-index (SI)-core waveguides with the same materials by means of the same process. Then, we evaluate the inter-channel crosstalk in the SI- and GI-core waveguides under almost the same conditions. It is noteworthy that remarkable crosstalk reduction (5 dB and beyond) is confirmed in the GI core waveguides, since the propagating modes in GI-cores are tightly confined near the core center and less optical power is found near the core-cladding boundary. This significant improvement in the inter-channel
crosstalk allows the GI-core waveguides to be utilized for extra high-density on-board optical interconnections.

High-density channel alignment of graded index core polymer optical waveguide and its crosstalk analysis with ray tracing method

HSU HSIANG-HAN, ISHIGURE TAKAAKI

Optics Express (Optical Society (OSA)) 18 ( 13 ) 13368-13378 2010.06

Research paper (scientific journal), Joint Work

We fabricate graded index (GI) multi-channel polymer optical
waveguides comprised of poly methyl methacrylate(PMMA)-poly benzyl methacrylate copolymer for the purpose of achieving high thermal stability
in the GI profiles. The waveguides obtained show slightly higher propagation loss (0.033 dB/cm at 850 nm) than doped PMMA based GI core polymer waveguides we have reported, due to the excess scattering loss inherent to the mixture of copolymer and homo-polymer in the core area. In this paper, we focus on the influence of the excess scattering loss on mode conversion and inter-channel crosstalk. We simulate the behavior of light propagating inside the core with and without the scattering effect.
Using the simulation, the excess loss experimentally observed in the copolymer-core waveguide is successfully reproduced, and then, we find that the excess scattering loss of 0.008 dB/cm could increase the inter channel crosstalk from −30 dB to −23 dB which agrees with the
experimentally observed value. Although the simulation of the inter channel crosstalk was performed only on our GI-core polymer optical waveguides, it is capable of modeling the conventional SI rectangular-core waveguides. Some amount of excess scattering is generally observed in the conventional SI-core waveguides, and thus, the application of this simulation to SI-core waveguides allows a feasible design for high-density alignment of the waveguides.

Carbon Nanotube-Doped Polymer Optical Fiber

UCHIDA　SHO,　AMOZ MALTINEZ,　SONG　YON　DON, ISHIGURE TAKAAKI,　YAMASHITA SHINJI

Optics Letters (Optical Society (OSA)) 34 ( 20 ) 3077-3079 2009.10

Research paper (scientific journal), Joint Work, Accepted

Polymer parallel optical waveguide with graded-index rectangular cores and its dispersion analysis

KOSUGI　TOMOYA, ISHIGURE TAKAAKI

Optics　Express (Optical Society (OSA)) 17 ( 18 ) 15959-15968 2009.08

Research paper (scientific journal), Joint Work, Accepted

High-Density 2 X 4 Channel Polymer Optical Waveguide with Graded-Index Circular Cores

YUSUKE TAKEYOSHI, ISHIGURE TAKAAKI

Journal of Lightwave Technology (IEEE/OSA) 27 ( 14 ) 2852-2861 2009

Research paper (scientific journal), Joint Work, Accepted

Fabrication of Carbon nanotube poly-methyl-methacrylate composites for nonlinear photonic devices

ISHIGURE TAKAAKI

Optics Express (Optical Society of America) 16 ( 15 ) 11337-11343 2008.07

Research paper (scientific journal), Joint Work, Accepted

Polymer Parallel Waveguide with Circular W-shaped Index Profile Cores

TAKEYOSHI YUSUKE / ISHIGURE TAKAAKI

IEEE Photonics Technology Letters (IEEE) 19 ( 22 ) 1795-1797 2007.11

Research paper (scientific journal), Joint Work, Accepted

Densely Aligned Multichannel Polymer Waveguide With Low Inter-Channel Crosstalk

TAKEYOSHI YUSUKE　/　ISHIGURE TAKAAKI

IEEE Photonics Technology Letters (IEEE) 19 ( 19 ) 1430-1432 2007.10

Research paper (scientific journal), Joint Work

屈折率分布型円形コアを有するポリマー並列導波路は，従来の均一屈折率コア型導波路に比べて，屈折率分布によりコア部への光の閉じ込め効果が強く，従って，より高密度に並列配線を施しても，チャネル間のクロストークが十分に低減できることを実験的に明らかにした．また，コア部への光の入射位置ずれに対しても許容が大きく，低クロストークを保てることを確認した．

Polymer waveguide with 4-channel graded-index circular cores for parallel optical interconnects

ISHIGURE TAKAAKI　/ 　TAKEYOSHI YUSUKE

Optics Express (Optical Society of America) 15 ( 9 ) 5843-5850 2007.04

Research paper (scientific journal), Joint Work, Accepted

ハイエンドルータやサーバ，HPCなどの筐体内光インターコネクションを実現する低損失で高密度・高速伝送ポリマー並列光導波路を初めて提案した論文である．従来型のポリマー導波路は半導体プロセスによる作製法をベースとしているため，コア部が矩形で均一屈折率コアを有するが，本提案の導波路は，円形で屈折率分布型コアを有する．このため，従来導波路に比べ，十分な低損失性と広帯域性，さらに，強いコア部への光閉じ込め効果を有することを示した．

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